docs: def decimal_year(year, month, day):
      """
      Allows to calculate the decimal year for a vector of dates
      (TODO this is legacy code kept to maintain comparability with previous
      declustering algorithms!)
  
      :param year: year column from catalogue matrix
      :type year: numpy.ndarray
      :param month: month column from catalogue matrix
      :type month: numpy.ndarray
      :param day: day column from catalogue matrix
      :type day: numpy.ndarray
      :returns: decimal year column
      :rtype: numpy.ndarray
      """
      marker = np.array([0., 31., 59., 90., 120., 151., 181.,
                         212., 243., 273., 304., 334.])
      tmonth = (month - 1).astype(int)
      day_count = marker[tmonth] + day - 1.
      dec_year = year + (day_count / 365.)
  
      return dec_year